Auditory prostheses not only bring a high level of functional hearing to deafened patients, but can also be a powerful tool for auditory neuroscience. Given the minimal and distorted cues provided by these devices, what factors allow some patients to recognize speech while others cannot? This proposal achieves leverage on this question by comparing psychophysical and speech performance across patient etiologies, patient performance levels, and across implant locations: cochlea, cochlear nucleus (CN), and inferior colliculus (IC). The long-term goal of this proposal is to utilize prosthetic activation of different stages in the human auditory system to understand how different levels of auditory processing contribute to speech pattern recognition. Our primary hypothesis is that speech pattern recognition depends strongly on specific peripheral processing, and that damage to these peripheral elements degrades speech recognition even when most other perceptual elements appear to be normal. A secondary hypothesis is that psychophysical performance with simple stimuli is not a good predictor of speech performance with electric hearing; psychophysical measures with complex stimuli may utilize similar perceptual mechanisms used for speech recognition, and thereby better predict patient outcomes. The specific aims are: 1. To quantify perceptual measures that may reflect biophysics from electrical stimulation of surface and penetrating electrodes in the cochlea, cochlear nucleus, and inferior colliculus in deaf patients. 2. To compare performance on simple and complex psychophysical tasks in patients with surface and penetrating electrodes in the cochlea, CN, and IC. 3. To use the results from Aims 1 and 2 to develop a profile that distinguishes patients with good speech recognition from those with poorer levels of recognition. The psychophysical tasks that correlate with speech recognition, obtained from electrical stimulation at three different levels of the auditory periphery, may help to define the perceptual characteristics of the putative peripheral damage. In addition, comparison of speech recognition and profiles of psychophysical performance will suggest links between basic perceptual capabilities and more complex auditory pattern recognition.